8.3 Membrane Transport [HY] Flashcards
How do small and large molecules go through cell membrane?
Transport of small nonpolar molecules occurs rapidly through the cell membrane via diffusion, while ions and larger molecules require more specialized transport processes.
What type of transport increases with temp?
- Diffusion, facilitated diffusion, and osmosis. Increase as temp. increases
Is active transport affected by temperature?
- active transport may or may not be affected by temperature, depending on the enthalpy (ΔH) of the process
What affects passive transport thermodynamically?
- an increase in entropy (ΔS)
Simple diffusion
- The most basic of all membrane traffic processes
- substrates move down their concentration gradient directly across the membrane
- Only particles that are freely
permeable to the membrane are able to undergo simple diffusion
Osmosis
- Water concentration moves down gradient from high to low
- Water solute concentration moves up gradient from low to high
Hypotonic
- If the concentration of solutes inside the cell is higher than the surrounding solution
- such a solution will cause a cell to swell as water rushes in, sometimes to the point of bursting (lysing).
Hypertonic
- A solution that is more concentrated than the cell
- water will move out of the cell
Isotonic
- If the solutions inside and outside are equimolar
- prevents the net movement of particles
Osmotic pressure
- a colligative property
- a physical property of solutions that is dependent on the concentration of dissolved particles
- II= iMRT [M is molarity. R is gas constant. i is van’t hoff factor, T is absolute temp.
- If the osmotic pressure created by the solutes within a cell exceeds the pressure that the cell membrane can withstand, the cell will lyse.
What does osmotic pressure formula tell us?
- directly proportional to the molarity of the solution
- osmotic pressure,
like all colligative properties, depends only on the presence and number of particles in solution, but not their actual identity.
Semipermeable membrane
- refers to a membrane governed by the same permeability rules as biological membranes: small, nonpolar, lipid-soluble particles (and water) can pass through freely, while large, polar, or charged particles cannot
Facilitated Diffusion
- simple diffusion for molecules that are impermeable to the membrane (large, polar, or charged)
- requires integral membrane proteins to serve as transporters or channels for these substrates.
- Channels are also viable for facilitated diffusion
Occluded state
- When the carrier is not open to either side of the phospholipid bilayer
- Binding of the substrate molecule to the transporter protein induces a conformational change and the carrier is briefly in this state
How do channels in an open conformation work?
- exposed to both sides of the cell membrane and act like a tunnel for the particles to diffuse through, thereby permitting much more rapid transport kinetics.
Primary active transport
- uses ATP or another energy molecule to directly power the transport of molecules across a membrane.
- involves the use of a transmembrane ATPase
Secondary active transport (coupled transport)
- uses energy to transport particles across the membrane; however, in contrast to primary active transport, there is no direct coupling to ATP hydrolysis. Instead, secondary active transport harnesses the energy released by one particle going down its electrochemical gradient to drive a different particle up its gradient.
Symport
When both particles flow the same direction across the
membrane
Antiport
When the particles flow in opposite directions
Pinocytosis
- the endocytosis of fluids and dissolved particles
Phagocytosis
the ingestion of large solids such as bacteria
*via clathrin coated vesicles
